In a well pumping apparatus, it is customary to employ a stuffing box at the wellhead to prevent oil, water and gases produced under pressure by the pumping apparatus from escaping into the atmosphere. Generally, the stuffing box is disposed in surrounding relation to the polished rod in order to guide or center the polished rod for vertical reciprocal movement or for rotation without the escape of produced liquids or gases. Typically, the stuffing box is able to prevent the loss of produced liquids and gases by utilization of a series of packing coils which are compressed within the stuffing box by bearings at opposite ends of the coils and are squeezed or otherwise forced against the coils by a threaded end member. The stuffing box is connected directly into the well production string, for example, by threading the lower end of the stuffing box into a conventional flow tee or pipe fitting.
Typical packing seals comprise split seals of woven or fibrous materials and the like which require compression for effecting a good seal around the polished rod. Typical examples of packing seals in stuffing boxes can be found in U.S. Pat. No. 5,058,668 belonging to Newton and U.S. Pat. No. 6,412,783 belonging to Finnestead and Canadian patent application 2,591,288 belonging to Smith International Inc. Due to the compression required to effect a good seal, it is common for these types of seals to wear quickly and to lose their sealing ability due to overheating from relative movement of the polished rod against the packed seals. When relying solely on such packing type seals as noted in the cited examples above, poor sealing performance is achieved and there is concern for damage to the polish rod or the housing of the stuffing box due to debris entering the stuffing box due to the movement of the polish rod.
To prevent the entry of debris, a scraper ring may be provided such as disclosed in U.S. Pat. No. 4,345,766 belonging to Turanyi. While the scrapers assist in preventing large debris from entering into the housing of the stuffing box, the configuration of the scrapers provide no assistance to sealing against the polish rod for containing the pressure in the well.
Canadian patent 2,452,696 belonging to Baycroft discloses another example of a stuffing box housing in which sealing is provided solely by packing seals under compression within the housing between bushings at opposed ends of the housing. The bushings are arranged for engaging the polish rod directly which may be of concern for wearing due to the design of the bushings. The patent to Baycroft is concerned primarily with a rubber sealing ring at the bottom of the housing which is only useful for engaging the rod coupler of the polish rod when flushing the well due to the interior of the diameter of the sealing ring being arranged to be greater than the diameter of the polish rod so that no sealing engagement is provided therebetween.